This invention relates to data storage disks and, in particular, to a tool for applying a metal hub plate to a hub of a data storage disk.
With the miniaturization of various electronic devices, such as personal electronic devices (PEDs) and digital cameras, a suitable storage medium capable of storing the large quantities of data required by these devices is needed. Magnetic storage devices typically do not have the required capacity. Flash memories have sufficient capacity, but the cost per megabyte is prohibitive for most applications. Compact discs (CDs) and digital versatile disks (DVDs) are generally too large for use with these very small devices.
Accordingly, it would be desirable to have an optical disk that is small (for example, between 25 and 40 mm in diameter) and that is recorded on both sides. This would take advantage of: (1) the recording density available on optical disks, (2) the permanence of optically recorded data, and (3) the capacity allowed by having the data stored on both sides of the disk.
A number of problems must be solved to make such a storage disk a reality. To permit recording on both sides of the disk, the data must be stored on the xe2x80x9cfirst surfacexe2x80x9d of the disk, i.e., the surface facing the read-write head, rather than the xe2x80x9csecond surfacexe2x80x9d, as is the case with CDs and DVDs. The disk must be mounted on the spindle of the disk drive in a highly repeatable manner and in a manner that permits a very accurate alignment between the axis of the rotation of the spindle and the geometric center of the data tracks on the disk (whether the tracks are spiral or circular). Otherwise, undue run-out will be experienced and tracking will be difficult. Moreover, since the data patterns on the opposite sides of the disk are not normally coincident, separate axes of rotation are required depending on which side of the disk is being read. The disk must also be mounted very accurately in a direction perpendicular to the recording surface to allow the read-write light beam to be accurately focused on the recording surface. The profile of the disk in the direction of the axis of rotation should be as small as possible to minimize the equivalent dimension of the electronic device. A method must be provided to clamp the disk to the spindle securely enough to prevent slippage when the spindle motor accelerates the disk, but without physically deforming the disk.
The above-referenced application Ser. No. 09/560,781, now abandoned, describes a hub assembly which includes a hub member, typically made of plastic, and a metal washer or hub plate that is attached to the hub member. The hub plate is made of a metal, such as a mild steel, that is magnetically attractive. The hub assembly is loosely fitted within the central hole of a data storage disk, allowing the hub assembly to be adjusted with respect to the disk in order to align a central bore of the hub assembly with the geometric center of the data tracks on the disk. Two hub assemblies are attached to opposite sides of the disk, each hub assembly being positioned concentrically with respect to the data tracks on one side of the disk. A magnet is positioned in the disk drive, and the magnetic force between the magnet and the metal hub plate is used to clamp the hub assembly and attached disk to the spindle of the disk drive. Alternatively, the plate itself may be made of a magnetic material.
As pointed out in application Ser. No. 09/560,781, since the plastic hub member and metal hub plate have different thermal expansion coefficients, to avoid unwanted fracturing or distortion of the plastic hub member the hub member must be allowed to expand or contract relative to the metal hub plate. This is accomplished by providing the metal hub plate with four tabs which are bent around the hub member. The tabs are located at right angles with respect to each other around the perimeter of the metal hub plate. After bending, each of the tabs fits into a slot or notch in the plastic hub member in a way that allows the hub member to expand or contract, while contact between the sides of the four tabs and the sidewalls of the notches positions the metal hub plate accurately with respect to the hub member. Since the tabs are only, for example, 1 mm wide, any differential thermal expansion between the tab and the metal hub plate in a direction transverse to the tab is not sufficient to fracture or distort the hub member.
Thus, when the hub assembly is attached (e.g, with a UV-curable adhesive) to a data storage disk, the alignment between the central bore of the metal hub plate and the geometric center of the data tracks is fixed while the plastic hub member is allowed to expand or contract with respect to the metal hub plate as the temperature of the disk and hub assembly varies. To avoid undue wear, the central bore of the plastic hub member is preferably made slightly larger than the central bore of the metal hub plate, and the spindle of the disk drive is fitted into the central bore of the metal hub plate. The hub member is preferably made of the same material as the disk, or at least a material which has a very similar coefficient of thermal expansion. Therefore, differential thermal expansion between the hub member and the disk is not a problem.
According to this invention, a crimping tool is described for mounting the metal hub plate onto the plastic hub member. In order for the hub assembly to perform satisfactorily, several conditions must be met: (1) the tabs of the metal hub plate must fit securely against the sidewalls of the notches in the hub member to fixedly position the metal hub plate with respect to the hub member; (2) there must be enough clearance between the tabs and the metal hub plate to allow differential thermal expansion between the hub member and the metal hub plate (i.e., the metal hub plate must not be clamped too tightly against the hub member); (3) the process of bending the tabs should create no burrs on the surface of the tabs; (4) after the bending is completed, all portions of the tabs should be depressed into the notches so that the hub member can be bonded to a disk without interference from the tabs.
A crimping tool according to this invention includes plunger having a central axis and being moveable along said central axis. The plunger comprises a plurality of crimping jaws positioned radially with respect to said central axis, the crimping jaws being subjected to a force such that said crimping jaws project from an end of said plunger. The plunger also includes a plurality of surfaces oriented at an acute angle with respect to said central axis, each of said crimping jaws being slidable on a respective one of said surfaces such that when one of said crimping jaws slides on said respective one of said surfaces, the motion of said crimping jaw has a first component parallel to said axis and a second component perpendicular to said axis. The surfaces are oriented such that the crimping jaws move towards the central axis when said crimping jaws are moved in a direction opposite to the force. A die is positioned in the tool such that the crimping jaws contact said die when said plunger is displaced a distance from a retracted position in the direction of said force along said axis.
The die comprises a cavity for retaining said metal hub plate.